It is well known that halogenated polymers such as PVC may be heat stabilized by combinations of divalent metal carboxylates, phenolic antioxidants, beta-diketones, phosphite salts, and hydrotalcite-like scavengers. U.S. Pat. No. 4,221,687 and 5,084,499 are examples of patents disclosing such stabilizers.
These types of stabilizer systems, where the metal carboxylates are based on zinc and alkaline earth metals, are useful in replacing stabilizers based on toxic metals such as cadmium or lead. In general, such calcium/zinc and barium/zinc stabilizers are not totally equivalent to lead or cadmium stabilizers in properties and processing. For example, heat stability is typically reduced with such zinc/barium or calcium stabilizers at elevated temperatures often encountered in processing vinyl halide resins at about 200.degree. C.
Antimony carboxylates are too unstable to be used as heat stabilizers in PVC. Antimony mercaptides, such as antimony tris (isooctyl thioglycolate) are well known as PVC stabilizers with reference to U.S. Pat. No. 2,680,726. Recently, it has been suggested that antimony mercaptides do not typically function in PVC directly as stabilizers, but rather as phase transfer catalysts for efficient stabilization by metallic carboxylates, for example, calcium stearate, "MIXED METAL VINYL STABILIZER SYNERGISM. IV: ANTIMONY MERCAPTIDE/GROUP II METAL CARBOXYLATE BLENDS" by R. F. Grossman, Antec, pages 2228-2290 (1992). Antimony oxide has been used for many years in PVC for improving flame resistance, but has not been reported as conferring increased heat stability.